Abstract
Image measurement methods have been widely used in broad areas due to their accuracy and efficiency. However, current techniques usually involve complex calibration, an elaborate optical design, or sensitivity to the test environment. In this paper, a simple optical device was designed to emit parallel beams to obtain a virtual scale for measurement purposes. The proposed theory ensures the robustness of the system when obtaining each scale in the presence of uncertainty. The scale creates a mapping from image coordinates to world coordinates. By using the moving least squares (MLS) method, a full-field scale map can be reconstructed to achieve high-precision measurement at the sub-pixel level. Experimental verifications are carried out, showing that the proposed method provides very accurate and reliable results. The proposed approach is simple in terms of equipment, and the scale can be automatically calculated. Therefore, the system proposed in this paper is a promising candidate as a tool for non-contacting measurements (e.g., the crack development, geometric size) in the inaccessible structures such as high-rise buildings and long-span bridges.
Highlights
Modern industry requires higher accuracy and efficiency for geometric measurement instruments [1]
In the last few decades, optical technology as a non-contacting measurement technique has been wildly used in broad areas
The optical measurement techniques fall into two categories [2]: the methods that use laser beams, such as laser doppler vibrometry [3], electronic speckle pattern interferometry (ESPI) [4], and digital speckle shearography (DSS) [5]; and the methods that use white light, which is called photogrammetry or image measurement method
Summary
Modern industry requires higher accuracy and efficiency for geometric measurement instruments [1]. The accuracy of the DIC method is closely related to the quality of the speckle pattern, environmental vibration, and camera calibration [12] These factors limit the application of the DIC method, such as crack development in bridges and high-rise buildings, where on-site environmental vibration continually occurs and some structures are inaccessible. As for the target-less method, researchers utilize the internal features or edges of a structure to recognize the object or areas of the object that needs to be tracked This method is especially useful when it is impossible to mount optical targets to the structure or spray the speckle pattern on the surface. The accuracy of the current measurement techniques usually relies on the intrinsic and extrinsic parameters of the system, which requires a strict calibration process [13,14] To this end, we propose a simple laser setup for non-contacting two-dimensional measurements. We present two experiments to verify the proposed method
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